1. Field of the Invention
The present invention relates to a printing apparatus providing a function of printing a test pattern for the purpose of inspecting a printing state of each of a plurality of print elements composing a print head, and a printing method of this test pattern.
2. Description of the Prior Art
Up to now, in a printing apparatus such as an ink jet printer that uses a print head having a plurality of ink ejection openings as a print element, an ejection failure such as clogging of the ejection opening may arise due to bubbles remaining inside the ejection opening or adhesion of ink drops and dust near the ejection opening during a printing operation. Therefore, it is desirable to periodically inspect an ejection state of the ejection opening so as to always maintain the optimum ejection state. In a conventional inspection method, it is common to print a certain test pattern and decide whether or not an ejection failure exists by the print result.
Furthermore, if the ejection failure is found by means of such an inspection, the process of removing the cause of the ink ejection failure is performed by performing recovery processing such as a preliminary ejection process and a suction recovery process.
An example of a test pattern printing method is discussed in Japanese Patent Publication No. 6-78019 (1994). This method comprises the following steps. A horizontal line having a certain width is printed by means of an ejection opening that is a most upper position in order of arrangement within print a head, then a vertical line is printed by means of all the ejection openings of the head. Thereafter, in a similar fashion, a horizontal line having a certain length is printed by means of an ejection opening using the second ejection opening from the most upper one, and then, a vertical line is printed by using all the ejection openings. Thus, an ejection opening, which prints a horizontal line is shifted, every ejection opening so that a stepped test pattern is printed. Then, if a part of this test pattern lacks, it can be determined which ejection opening corresponding to the part that has failed during ejection. Nevertheless, if this test pattern is printed in a color with comparatively low visibility such as yellow, it is difficult to clearly separate a part, which is correctly printed, from a ground color of a printing medium such as paper. Therefore, if a defective part exists in this situation, it is difficult in some cases to identify a defective part.
To address this drawback, a test pattern printing method, mentioned in Japanese Patent Application Laid-Open No. 9-66650 (1997.) uses a stepped test pattern that is similar to the method described above, but enhances visibility in regard to a color with comparatively low visibility by overlaying another color on this color with comparatively low visibility at the same location. For example, by overlaying a cyan pattern on a yellow pattern, a green pattern is printed. In this case, if a part of the yellow pattern is defectively printed, the defective part is not printed in green, and hence is printed only in cyan.
Nevertheless, the test pattern printing method described above has the following problems.
Thus, some of recent printing apparatuses can improve a gradation in an image and decrease a granular texture by using low-concentration ink (i.e., low-density ink) in addition to normal-concentration ink and can perform printing in high resolution by down-sizing an ink drop ejected from an ejection opening so as to down-size a dot printed, according to a request for high-quality printing.
In this case, in a print head using the low-concentration ink, even if the test pattern described above is applied, it may be difficult to discriminate between a part correctly overlaid and a part where a dot-of the low-concentration ink lacks due to brightness of the low-concentration ink itself and the like. For example, if low concentration magenta (hereinafter, this is called light magenta) and low-concentration cyan (hereinafter, this is called light cyan) is overlaid, blue is formed. Nevertheless, since this blue is in low concentration, this color itself is also in low visibility. Therefore, difference between the part where, blue is formed and the part where only cyan is printed is not clear.
In addition, in the test pattern in case of small dot diameter, an effective area of each dot is small, and hence it sometimes may be not possible properly recognize whether the dot has been printed regardless of the color and concentration of ink.
Furthermore, if the test pattern is in secondary color (overlay of a plurality of color) printed in a dot with small diameter and a defective dot is present, it may be not possible to readily determine what color is lacking.
An object of the-present invention is to provide a test pattern printing method that can adequately decide a print failure even in an apparatus performing printing in small dot diameter or printing in low-concentration ink, and a printing apparatus performing printing with such a method.
In a first aspect of the present invention, there is provided a test pattern printing method in a printing apparatus for printing an image on a printing medium, using a print head where a plurality of print elements for forming dots on the printing medium are arranged, the method comprising the steps of:
main scanning step for scanning the print head along a main scanning direction;
pattern printing step for selectively driving a plurality of print elements of the print head, thereby to form dots and print a test pattern, wherein the pattern printing step forms the predetermined number of dots along the main scanning direction according to the selected print elements, and the density of dots formed by each print element is higher than the print density caused during image printing operation.
In a second aspect of the present invention, there is provided a test pattern printing method in a printing apparatus for printing an image on a printing medium, using a print head where a plurality of print heads thereby to form dots on the printing medium are arranged, the method comprising the steps of:
scanning step for scanning the printing head relatively to the printing medium in a direction different from the plurality of print elements; and
test pattern printing for selectively driving the printing elements of the print head during scanning in the scanning step, thereby to print a test pattern, the test pattern printing step repeating the steps of: selecting predetermined print elements of the print head; and driving the selected print elements to form one or more lines along the scanning direction, thereby printing the test pattern, the lines being composed of a plurality 6f dots formed by the selected print elements,
wherein the test pattern printing step is capable of printing a plurality of test patterns that differentiate a method of forming dots constituting the test patterns, and the plurality of test patterns are different from each other in density of a plurality of dots constituting one or more lines along the scanning direction, respectively.
In a third aspect, of the present invention, there is provided a printing apparatus having main scanning means for relatively scanning along a main scanning direction a printing head where a plurality of print elements for forming dots on a printing medium are arranged, and driving the print elements of the print head during scanning by the main scanning means, thereby to print an image on the printing medium, the printing apparatus comprising:
test pattern printing means for selectively driving print elements of the print head during print head scanning by the main scanning means, thereby to print a plurality of test patterns, wherein the test pattern includes one or more lines printed along the main scanning direction by driving a selected, predetermined print element from among a plurality of print elements of the print head, and the lines are composed of a plurality of dots formed by the thus selected print element,
controlling means for controlling the density of a plurality of dots, wherein the dots constitutes the lines along the scanning direction of the test pattern, and the density is higher than the density caused during image printing.
In a fourth aspect of the present invention, there is provided a printing apparatus having main scanning means for relatively scanning along a main scanning direction a printing head where a plurality of print elements for forming dots on a printing medium are arranged, and driving print elements of the print head during scanning caused by the main scanning means, thereby to print an image on the printing medium, the printing apparatus comprising:
test pattern printing means for selectively driving print elements of the print head during print head scanning caused by the main scanning means, thereby to print a test pattern, wherein the test pattern includes one or more lines printed along the main scanning direction by driving one or more selected, predetermined print elements from among a plurality of-print elements of the print head, and the lines are composed of a plurality of dots formed by the thus selected print element, and
controlling means making it possible to print a plurality of test patterns that differentiate a method of forming dots constituting a test pattern, wherein a plurality of test patterns are different from each other in the density of a plurality of dots constituting the lines along the scanning direction.
According to the above construction, a plurality of dots are formed by means of the same print element so that the plurality of dots are overlaid with or contacted to each other, and thus the density of a dot pattern is increased or the area of a dot pattern is increased, which are formed by the same print element, on a printing medium. Therefore, the visibility of an overall test pattern is enhanced, and the abnormality of a print element can be easily detected.
The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.